On October 12, U.S. President Donald Trump is expected to announce whether his administration still finds Iran in compliance with the 2015 nuclear deal. Here's a look at what could happen if he chooses not to certify Tehran's compliance.

What is the Iran nuclear deal?

In July 2015, the permanent five members of the U.N. Security Council (Britain, China, France, Russia and the United States, plus Germany) agreed with Iran on a landmark deal to prevent Tehran from building a nuclear bomb. In exchange, certain international sanctions that have been in place against Iran for years would be lifted.

The sanctions relief led to Iran receiving billions of dollars in unfrozen funds and opened its markets back up to many foreign investors.

The Joint Comprehensive Plan of Action as it's known by its formal name or JCPOA — took years to negotiate and was endorsed by a United Nations Security Council resolution, solidifying it as international law. It went into effect in January 2016.

Inspectors from the U.N. nuclear watchdog, the IAEA, are in charge of monitoring Iran's compliance.

The parties also established a Joint Commission to monitor implementation and handle disputes. Federica Mogherini, the European Union foreign policy chief, chairs it.

The deal's architects have hailed it as a success story for multilateral diplomacy. President Trump has dismissed it as an "embarrassment" and one of the worst deals into which Washington has ever entered. During his campaign, Trump said he'd like to tear it up.

Can he do that?

Not exactly.

The Iran nuclear agreement was reached during U.S. President Barack Obama's tenure and after it was approved, congressional Republicans tried to derail it.

FILE -Senate Foreign Relations Committee Chairman Sen. Bob Corker, R-Tenn., (C) and the committee's ranking member Sen. Ben Cardin, D-Md. speak to reporters on Capitol Hill in Washington, April 14, 2015, as the Senate muscled its way into President Barack

But under U.S. legislation adopted in the lead up to the finalization of the agreement, Congress gave itself review and oversight privileges for any nuclear deal reached with Tehran.

Under the Iran Nuclear Agreement Review Act of 2015 (INARA), the U.S. president must certify to Congress every 90 days that Tehran is abiding by the provisions of the deal.

Four criteria must be met:

1. Iran is transparently and verifiably fully implementing all parts of the deal

2. Iran has not committed a material breach of the agreement

3. Iran has not taken any action, including covert activities, that could significantly advance its nuclear weapons program

4. Suspension of Iran-related sanctions are appropriate and proportionate to measures taken by Iran to terminate its nuclear program and are vital to U.S. national security interests

If the president does not certify Iran's compliance this month, it would trigger a 60-day period in which Congress can introduce legislation to re-impose some or all of the old U.S.-imposed sanctions (but not the U.N. ones).

If that happens, it could cause problems with countries that have resumed trade and banking relationships with Iran, by forcing Washington to impose secondary sanctions on them for cooperating with Tehran.

Iran could also try to accuse the United States of having been the first to violate the deal and lead to its collapse.

Congress could also decide not to re-impose sanctions and nothing would change.

Will he or won't he?

President Donald Trump speaks in the Cabinet Room of the White House in Washington, Sept. 12, 2017.

So far, President Trump has certified the deal twice since taking office. The next deadline is October 15. Trump has repeatedly indicated that he is not inclined to find Iran in compliance, most recently on Thursday.

"The Iranian regime supports terrorism and exports violence, bloodshed, and chaos across the Middle East," the president said at a meeting with his senior military leaders. "That is why we must put an end to Iran's continued aggression and nuclear ambitions. They have not lived up to the spirit of their agreement and we will be discussing that tonight."

But "spirit" is different from obligations, and the IAEA has repeatedly verified that Iran is adhering to its obligations, most recently on August 31, 2017.

In September, on the sidelines of the annual U.N. General Assembly, the parties to the agreement met, and the European Union's Mogherini said they all agreed Iran is in compliance.

"The agreement is concerning the nuclear program, as such it is delivering, we all agreed that all parties are fulfilling their commitments, the agreement is being implemented," she told reporters.

Some view that as a political strategy on the part of the president to show his supporters that he followed through on his promise to be tough on the Obama-era agreement, but without violating it.

But that has risks. Decertifying and sending the deal to Congress puts its future in jeopardy.

"This agreement is not something someone can touch," Iranian President Hassan Rouhani warned last month in New York. "This is a building, that from the frame of which if you take off a single brick, the entire building will collapse."

If the deal falls apart, Iran could decide to resume producing and enriching uranium.

Other parties to the deal say they will continue to uphold it.

"The UK, whatever the United States does, will continue to abide by this deal, as it is an important part of providing stability in that region," British Ambassador Matthew Rycroft told reporters.

European Union foreign policy chief Federica Mogherini answers questions during a news conference following a European Union-hosted meeting about the Iran nuclear deal at United Nations headquarters, Sept. 20, 2017.

The EU's Mogherini was also quite blunt, saying after her September meeting with the other parties that, "I can tell you as Europeans, we will make sure the agreement stays."

Worries about North Korea

U.S. allies are also nervous decertification or withdrawal could derail diplomatic efforts to get the North Koreans to come to the negotiating table to give up their nuclear program.

''We would be very concerned that if ... a major partner is not attached to the Iran agreement anymore — in this particular time — this would send a very problematic signal to North Korea and all those who we want to get into a political discussion with a political solution on North Korean issues," said a senior European diplomat.

The United States is the only party to the deal that has expressed an interest in renegotiating the agreement. France's president has suggested opening separate discussions on non-nuclear related issues, such as Iran's support for militias in Syria and Yemen, its ballistic missile activity, and the period after the nuclear agreement ends in 2025.

Bottom line

If President Trump decides to toss the Iran ball to Congress, he could inject a high degree of uncertainty into the process. While it remains unclear what Congress' intention is now, any action that could be perceived as a U.S. violation of the deal could have the unpleasant consequence of isolating Washington internationally.